The invention relates to a pocket filter having an outer frame made of plastics material and several adjacent filter elements arranged in the outer frame.
A known pocket filter of this type disclosed in German patent publication DE 44 43 144 C1 makes use of an outer frame of which the profiles exhibit a U-shaped inwardly opened cross section. At the end of each of the limbs of this cross section, a web extends inwardly at right angles. The clear distance between webs is smaller than the height of the profiles of the inner frame. Each of these profiles is rotated elastically around its longitudinal axis before it can be manipulated with the free border of the pocket into the interior space of the profile of the outer frame. To this end, the deformation resistance of the longitudinal and front profiles of each inner frame must be reduced by means of end notches, which has a disadvantageous effect on the rigidity of the inner frame. Longitudinal profiles of the inner frame are provided with holes and accompanying complementary, projecting parts protruding outwards. Each projecting part penetrates two pocket borders and one aligned hole in the adjacent inner frame and is finally welded to a rivet head. Transverse walls are arranged between the longitudinal profiles and between adjacent protruding parts and holes of each longitudinal profile. The low level of rigidity of the inner frame and the high assembly costs are disadvantageous.
The design of the outer frame in one piece in the form of a grid with a longitudinal opening for each filter pocket is known per se from U.S. Pat. No. 4,300,927 A. Each inner frame is designed as a funnel shape and, at the inlet side, is interlocked by means of teeth with an inner border of the outer frame.
An additional clamping ring presses the free border of the filter pocket against the outer surface of the inner frame.
U.S. Pat. No. 4,312,648 A shows as known per se a one-piece outer frame onto which outer flanges of funnel-shaped inner frames are placed in an overlapping manner. An additional clamping ring is also required here in accordance with U.S. Pat. No. 4,300,927 A.
One-piece inner frames made of plastics material with transverse walls between the longitudinal profiles are known per se from U.S. Pat. No. 5,298,044 A. The transverse walls laterally limit open-passages; in each case, a projecting part is arranged in the longitudinal center of one longitudinal profile, and a hole is arranged in the other longitudinal profile. The free border of two filter pockets in each case is clamped between adjacent inner frames and their projecting part/hole pairings. Each inner frame is supported with a continuous longitudinal flange in a continuous longitudinal groove of the adjacent inner frame. The facing profiles of the inner frame are held with projecting parts and the free borders of the filter pockets in an outer frame of U-shaped cross section.
Bending the outer frame from a metal strip with notches along the border is known per se from German patent publication DE 87 16 251 U1. In this context, overlapping areas with sections of the sheet metal folded at right angles are produced at the corners of the outer frame in order to achieve the most level outer facing surface of the outer frame possible. The outer frame ultimately has a U-shaped cross section.
In the case of a pocket filter known per se and disclosed in German patent publication DE 93 00 732 U1 all the profiles of the outer frame have a purely U-shaped, inwardly open cross section into which extensions of the corner connectors also exhibiting a U-shaped cross-section are adhered. The border of the filter pockets can be held firmly sealed in the interior space of the profiles of the outer frame with a sealing strip made of PU-foam or cellular rubber. This design is not sufficiently stable especially with relatively high pressure differences and larger filter-pocket sizes. The holding and sealing of the filter pockets in the outer frame are unreliable.
Designing all profiles of the outer frame with a U-shaped, inwardly opened cross section is known per se from U.S. Pat. No. 4,356,011 A. In the interior space, a stopping strip projects from approximately half of every limb; on closing the outer frame, the said stopping strips are placed against the free border of the filter pocket. This free border is inserted together with a bar of the inner frame into the outer frame. Longitudinal bars of adjacent inner frames are attached to one another by rivets with pocket borders clamped between them.
The present invention is based on the object of designing the inner frame to be more stable, and simplifying and improving the installation of the filter elements into the outer frame.
This object is resolved by a pocket filter according to the invention having an outer frame made of plastics material and several adjacent filter elements arranged in the outer frame. The outer frame is composed of opposing limb profiles, a base profile and a closing profile, each of which have an essentially U-shaped cross section with an inwardly opened interior space. Each of these elements can be joined to one another at the corners of the outer frame, wherein each profile of the outer frame exhibits a base wall and limbs extending from the base wall. Holding ribs extend from the free end of each limb and are spaced at a clear distance from one another.
An inner frame made of plastics material of the accompanying filter element is arranged within a free border of each filter pocket. Each inner frame exhibits two opposing longitudinal profiles and two opposing end profiles attached at the ends of the longitudinal profiles.
In a transverse plane of each inner frame at least two holes are spaced from one another and at least two, outwardly extending, complementary projecting parts are arranged alternately in each longitudinal profile, whereby each hole in one longitudinal profile is opposed by a projecting part in the other longitudinal profile. Transverse walls are fastened on the accompanying longitudinal profile and extend into an inlet of the inner frame. Each projecting part of the inner frame penetrates the free border of the accompanying filter pocket and the free border of an adjacent filter pocket and engages into the complementary hole of the inner frame belonging to the adjacent filter pocket. Each filter element engages with the free border of its filter pocket in a sealed manner into the interior space of the adjacent profiles of the outer frame, and one of the transverse walls extends at least approximately in alignment with each hole and each projecting part of the longitudinal profiles of each inner frame.
The pocket filter is especially intended for filtering air and other gases. All the profiles of the outer frame are preferably made of extruded plastics material, for example, highly impact-resistant polystyrene or other plastics materials capable of incineration. The inner frame can be readily manufactured and connected in a form-locking manner with the free border of the accompanying filter pocket. The transverse walls form a desirable stiffening of the inner frame and, moreover, define lines of action for the assembly forces which will have to be applied in order to fit the filter elements into the outer frame. The penetration of the projecting parts through the free border of the filter pocket is also made easier. Additionally, the free ends of each of the projecting parts can be pointed. Fitting together the projecting part and the hole produces an additional mutual stiffening of the joint between adjacent filter elements. The holes and projecting parts are preferably spaced from one another at the same distance.
Inner frames designed in one piece can be manufactured in a particularly cost-favorable and robust manner.
Each inner frame can be designed in two parts so that the transverse walls and the end profiles of both parts of the inner frame overlap and so that the mutually overlapping transverse walls and end profiles are attached to one another respectively in the region of overlap. This provides the advantage of being able to produce different required overall widths of the inner frame. Mutually overlapping transverse walls and front profiles can be fastened, for example, with staples, by gluing or by welding.
The design and interlocking teeth of the outer flange sections of one inner frame with notches of the adjacent inner frame such that each longitudinal profile of the inner frame exhibits at an inlet side of the inner frame an outer flange projecting outwards and periodically interrupted by a notch lead to a further mutual stiffening of the joint between adjacent filter elements. Furthermore, each outer flange section of an inner frame can engage in a notch of an adjacent inner frame, and on each inner frame, each outer flange section of one longitudinal profile is opposed by a notch of the other longitudinal profile.
An underside of each outer flange acts as a stop for the free border of the associated filter pocket (20) to effect a defined positioning of the filter pocket relative to the accompanying inner frame before the projecting parts of the inner frame penetrate the free border of the filter pocket creating a form-fit joint.
Each longitudinal profile of the inner frame may exhibit an inwardly extending inner flange at an outlet side of the inner frame. This increases the rigidity of the inner frame and leads to a desired turbulence in the flowing medium which is to be cleaned. In this manner, erosion of the filter pocket downstream of the inner frame is prevented.
Each holding rib extends from its limb in the direction of the base wall and are similar to barbs and co-operate particularly well with the filter elements.
At least one opposing surface of the profile can be arranged at a distance from the free end of each holding rib in the interior space, and this is favorable with respect to flow technology and leads to a good fastening and sealing of the filter elements in respect of the outer frame. For instance, each opposing surface can, on the one hand, be attached to the accompanying limb and, on the other hand, may be supported by a support web on the base or on an intermediate wall of each profile of the outer frame wherein the said intermediate wall defines the longitudinal channel. As a result, the profiles of the outer frame also gain additional rigidity even with a small wall thickness.
The filter element can be arranged respectively at the base profile and at the closing profile of the outer frame and exhibits an outer longitudinal profile facing the base profile or the closing profile to ensure that the filter element is held reliably in the outer frame. The holding ribs of the outer frame lock and hold their outer longitudinal profile in the optimum operating position.
This effect is also achievable with a shoulder of each transverse wall cooperating with free ends of the holding ribs in order to position and lock the filter element in place.
A wall of the filter pocket can be guided as if through a chicane and compressed between free ends of the inner flange and the opposing holding rib to ensure that a reliable holding of the filter pocket in the frame system is achieved and, additionally, in most cases, the filter pocket is adequately sealed in respect of the frame system.
If required, the free border of each filter pocket can be adhered to an outer surface of the accompanying inner frame to enhance the safety of the seal.
To also serve this purpose the filter pocket can be adhered both to the inner flange and also to the opposing limb and its holding rib (19).
Each filter element can be pushed into the limb profile of the outer frame in a simple manner such that each end profile and at least those regions of the longitudinal profiles of each inner frame which project into the intermediate space of the limb profiles of the outer frame exhibit a height which is somewhat smaller than the clear distance between the holding ribs of the limb profiles of the outer frame.
The filter pocket is generally already well sealed in respect of the frame system because the free border of each filter pocket is pressed by the two end profiles of the inner frame against the at least one opposing surface of the two limb profiles of the outer frame.
If required, this seal can be further improved if the free border of each filter pocket is adhered to the at least one opposing surface.
Further improvements to the holding and sealing of the filter pocket relative to the frame system may be realized if a wall of each filter pocket is guided as if through a chicane and compressed between lower edges of the longitudinal profiles of the inner frame and the opposing holding ribs of the limb profiles of the outer frame.
This effect can be further improved if each filter pocket is adhered to the opposing limb of the two limb profiles and also adhered to the holding rib of the limb.
The special type of corner connectors and their co-operation with the adjacent profiles of the outer frame allows the individual profiles of the outer frame to be connected to one another very easily, reliably and in a dimensionally stable manner. To that end a longitudinal channel is formed in the interior space of each of the profiles of the outer frame such that a tongue of an accompanying corner connector can be introduced from each facing side of the profile into the longitudinal channel of each profile so that each tongue exhibits a locking pin which snaps into a locking aperture in a wall of the longitudinal channel to achieve a form-fit locking of the corner connector and the profile. Initially only the two limb profiles are plugged into the base profile, thereby producing a U-shaped outer frame. The filter elements are then successively inserted into this. Finally, after the last filter element, the closing profile is connected via its two corner connectors to the adjacent limb profiles of the outer frame to form a complete, rigid outer frame. A relatively narrow fit which promotes stability may be established between the tongue of each corner connector and the accompanying longitudinal channel in the adjacent profile.
Each tongue may exhibit a transverse slot extending from its free end beyond the locking pin, and thus a form-fit locking of each corner connected to the adjacent profiles is achieved. This again increases the strength and rigidity of the overall outer frame. This form-fit locking is releasable. To this end, the part of the tongue which bears the locking pin can be pressed in elastically with a tool, for example, a screw-driver, until the locking pin has left the locking aperture. The corner connectors and profile are then separated.
A form-fit, releasable connection is achieved between the corner connector and the adjacent profiles if each tongue exhibits on each side of the locking pin a longitudinal slot extending from the free end of the tongue (10) to beyond the locking pin such that between the longitudinal slots a resilient lever bearing the locking pin is defined, and that the lever exhibits a recess in its side facing away from the locking pin for reducing its thickness by comparison with the thickness of the tongue.
By increasing the height of each locking pin in the direction towards a foot of the tongue production of the snap-connection is simplified. The height of the locking pin, for example, may start from zero. This results in a wedge-like design of locking pin which, when the corner connector and adjacent profile are pressed together, leads to a resilient deflection of the outer part of the tongue.
The longitudinal channel can be arranged adjacent to a base wall of the profile and support walls of the opposing surfaces are supported on an intermediate wall which defines the longitudinal channel. This leads to a particularly rigidly connected longitudinal channel and a correspondingly rigid outer frame altogether.
When the longitudinal channel is arranged adjacent to a base wall of the profile, and an intermediate wall opposing the base wall is corrugated in cross section such that a corrugation peak of the intermediate wall accommodates free ends of the adjacent projecting parts in a notch, and corrugation troughs of the intermediate wall are interspaced at a distance from one another define the opposing surfaces then a simplification in the manufacture of the profiles is achieved with adequate or even increased stability of the profiles.
Opposing guide-ribs of the profiles which guide the tongues project into the interior space of the profiles to facilitate the movement of the tongues in the interior spaces. The guide ribs are preferably arranged parallel to the direction of introduction of the tongues.
Each tongue may exhibit a substantially U-shaped cross section with a base and with side walls projecting inwardly from the base in order that an additional stiffening of the tongues is achieved.
A stiffening rib can extend from the base of each tongue in its longitudinal direction to achieve the same goal.
Gliding ribs which are spaced from one another and can be supported on a base wall of the profile can extend from each tongue and simplify and improve the movement of the tongue in the interior space of the profiles. The gliding ribs are preferably arranged parallel to the direction of introduction of the tongues.
The corner connector can exhibit a base element which bears the tongues and the base element exhibits lateral locating ribs which project in the direction of the profile and are intended for positioning on the accompanying profile to achieve a better seal of the base element in respect of the profiles of the outer frame.
Each projecting part can form a press-fit with the accompanying hole of the adjacent inner frame to achieve an additional stiffening of the joint between adjacent inner frames.
These and other features and advantages of the invention are explained in greater detail with reference to the embodiments shown in the drawings.